Statements and expressions - java

ABCs of Programming A java program is made up of classes and objects, which are made up of methods and variables. Methods are made up of statements and expressions – the smallest elements of java programming. Looking at the basics of Java code Statement – simple command that causes something to happen int weight – 225; System.out.println (“Lincoln High School is cool!”); song.duration = 230; Statement that produces a value is an expression The value produced is the return value Statements are terminated with a semicolon ;

Statements - continued In theory, more than one statement can be put on a line, best not to. Statements are grouped using an opening brace { and a closing brace } A group of statements between the characters is a block.

Variables and Data Types Java has three kinds of variables Instance variables – define an object’s attributes Class Variables – define the attributes of an entire class of objects Local Variables – only used inside a method We will work with local variables first. In java, you must create a variable by giving it a name and declaring its type. The type is listed first, followed by the name. EXAMPLES: int loanLength; String message; boolean gameOver;

Variables and data types EXAMPLES: int loanLength; String message; boolean gameOver; int represents integers String is an object that holds text boolean is used for Boolean true/false values Local variables can be declared at any place inside a method, BUT, they must be declared before they can be used. You can create several variables of the same type on the same line. String city, street, state;

Variables - continued Variables can be assigned a value when created by using an equal = sign followed by the value. You must give values to local variables before you use them in a program, or the program won’t compile successfully. NAMING VARIABLES – Names must start with a letter, an underscore character _ or a dollar sign $ Variables CANNOT start with a number. camelCase naming convention is best.

Comments Comments are essential to good programming. Comments help to organize and provide information for you and those working with you I require that all programs be properly commented – get used to it!! Single line comment two slashes // Everything from // to end of line is a comment Multi-line comments begins with /* and ends with */. Everything between them is a comment